1. Field of the Invention
The present invention relates to an air-permeable water non-permeable device, to which an air-permeable water non-permeable unit (assembly), which uses an air-permeable water non-permeable sheet (water-repellent microporous material), is mounted.
2. Description of Related Art
An air-permeable water non-permeable sheet (membrane member/film member), through which liquid is not allowed to pass and air (gas) is allowed to pass, is known in the art, for example, as a PTFE (polytetrafluoroethylene) microporous membrane. Such an air-permeable water non-permeable sheet can be provided, for example, to close up a through-hole in a housing, defining a space requiring ventilation (ventilation-requiring space), to be used for allowing gas to flow therethrough between this ventilation-requiring space and an external space while preventing liquid from permeating into the ventilation-requiring space (Japanese Unexamined Patent Publication No. 2009-78866).
In Japanese Unexamined Patent Publication No. 2009-78866, a special structure is proposed in the case where an air-permeable water non-permeable sheet is fixed around the periphery of a housing through-hole. On the other hand, another type of air-permeable water non-permeable sheet is also known in the art in which the air-permeable water non-permeable sheet is retained by a unit that is separate from a housing and the unit is mounted (detachably attached) onto a housing through-hole, without directly fixing the air-permeable water non-permeable sheet onto the periphery of the housing through-hole.
However, in a type of air-permeable water non-permeable device of the related art in which an air-permeable water non-permeable sheet is retained by a unit that is separate from a housing and the unit is mounted onto a housing through-hole, the balance between the mounting operability and the stability (ability to prevent the unit from falling out) upon the unit (to which the air-permeable water non-permeable sheet is fixed) being mounted is poor, so that there is a problem with the unit easily falling out in the case where the unit can be easily mounted, and with the unit being difficult to mount in the case where the unit does not easily fall out.